The present invention generally relates to novel encapsulation compositions and methods. In particular, the invention relates to fluorescent microcapsule compositions which comprise a layer of a polymer shell enclosing one or more particles capable of emitting at least two distinct fluorescent signals, and methods for their preparation. The compositions and methods of the invention are useful in a variety of applications, including preparation of arrays for industrial, chemical, immunological, and genetic manipulation and analysis.
Fluorescently labeled particles are being used extensively in a wide range of applications. By combining two or more dyes and by, varying each of fluorescent dyes"" concentration and/or the emission wavelengths of the dyes, it is possible to create an almost infinite number of fluorescently distinguishable particles. These particles can subsequently be used as markers in such diverse applications as combinatorial chemistry, diagnostics, e.g., DNA analysis, and industry uses, e.g., liquid labeling of fluids.
One such technology, which is currently available, uses polystyrene microspheres into which are absorbed precisely controlled quantities of two or more fluorescent dyes. This requires dissolution of the dye in an organic solvent, which can then be added to the microspheres, thus inducing swelling of the particle and absorption of the dye. The microspheres are then isolated from the dye solution and excess dye removed by a wash step. However, there are several drawbacks to this system. The first is that the wash step usually removes some of the dye from the beads, which makes it difficult to predict the exact amount of dye to be absorbed. Another problem is that placing these dyed microspheres in organic solvents results in leaching of the dye into the surrounding environment. Additionally, this technique requires that the dye be soluble in an organic solvent, which precludes the use of water-soluble particulate fluorescent materials. It would therefore be a significant improvement if methods were devised to encapsulate a precisely controlled number of soluble or insoluble fluorescent particles or substances within a stable shell material encapsulating them.
Encapsulation is a well-known technique in the art for protecting components that are sensitive to the elements, for providing controlled release of capsule ingredients, and/or to prevent dust formation by non-encapsulated particles among many other applications.
U.S. Pat. No. 5,879,920 issued to Dale et al., discloses multi-layered enzyme-containing composition, which is coated with a vinyl polymer. This composition, which is intended to be used as a laundry detergent, is useful for preventing enzyme-containing dust formation that may be allergenic to those who handle it. Among many other substances, fluorescent dyes are described as adjunct ingredients that may be added to the enzyme powder. However, no combination of fluorescent dyes is described or suggested. The only reason for using fluorescent dyes in detergents is to make laundered fabrics look brighter. Finally, the polymer shell of the enzyme granule must be readily soluble in an aqueous solution to release the enzyme and additive such as a fluorescent dye.
U.S. Pat. Nos. 4,724,094 and 4,341,997 issued to Song and Borrows respectively, disclose methods of preparing a fluorescent magnetic composition useful for inspecting and detecting cracks and various small defects in metal work pieces. The preparation of such fluorescent/magnetic particles is spread on the surface of a metal piece and defects are identified under ultra-violet light or xe2x80x9cblackxe2x80x9d light. The manufacturing of these particles involves a plasticizer in order to effect a more complete encapsulation of fluorescent pigment and magnetic particle powder by film-forming resin. Composition made by the inventive method are described, as well as methods of using the composition in non-destructive testing of magnetizable work pieces. This invention is not functional without magnetic particles and it does not require more than one fluorescent dye.
U.S. Pat. No. 4,534,317 issued to Walsh discloses two types of encapsulated food pellets containing fluorescent dyes. The first type, which when eaten by fish, causes the water to fluoresce, the second type disintegrates spontaneously causing the water to fluoresce when not eaten by fish. By administering food containing both types of fluorescent dyes simultaneously, and measuring the ratio of their respective fluorescence intensities, a sensitive measure of feeding activity is achieved. While two fluorescent dyes are used in this invention they are not present in the same capsule and ultimately these dyes are meant to be released in the aqueous environment.
The encapsulation techniques are also used in an unrelated field of entrapping of living cells in tiny microcapsules, which are then introduced into a host organism as a means of delivery of biologically important factors produced by such cells. Examples of microencapsulation devices can be found in U.S. Pat. No. 5,182,111, issued to Aebischer et al.; U.S. Pat. Nos. 4,487,758, 4,673,566, 4,689,293, and 4,806,355, each issued to Goosen et al.; U.S. Pat. No. 4,803,168, issued to Jarvis, Jr.; U.S. Pat. Nos. 4,352,883 and 4,391,909, both issued to Lim; U.S. Pat. No. 4,298,002, issued to Ronel et al.; and U.S. Pat. No. 4,353,888, issued to Sefton. However, the purpose and scope of these devices are not related to the instant technical field and thus the interior of these microcapsules does not contain fluorescent dyes.
The present inventor has provided a novel principle of encapsulating fluorescent materials in light-permeable, environment-stable capsules capable of emitting at least two distinct fluorescent signals.
This invention relates to the field of encapsulation whereby particles enclosed in a shell barrier are produced and said particles are capable of emitting two or more fluorescent signals. The invention relates to composition and methods of manufacturing particle-enclosing capsules. The particles themselves as a composition of matter comprises a precise mixture of a number of fluorescent materials, e.g., fluorescently distinct microspheres, crystals, nanocrystals, powders, liquid crystals, and the like, which are then encapsulated within a barrier or shell material.
The preferred composition of the invention comprises two or more substances, each substance capable of emitting a distinctive fluorescent signal and a shell barrier encapsulating these substances. It is preferable that fluorescent signals are distinctive by way of its wavelength, intensity, or both.
It is an object of this invention to provide a composition and methods of making such a composition available, whereby the composition contains fine fluorescent particles which are stable and capable of emitting discrete fluorescent signals during further processing of the composition, e.g., during flow cytometry analysis when exposed to a fluorescence excitation light. The invention relates to a composition containing fine fluorescent particles such as inorganic and organic spheres stained with discrete fluorescent dyes. These particles, besides being presented as spheres, may also presented in form of powders, crystals, rods, fibers, liquids, and the like, each encapsulated by a barrier to form a light-permeable capsule or dispersed in a matrix whereby the barrier and/or the matrix consists of a polymerizable material and, if necessary, of other additional components that will deter the leakage of the fluorescent dyes or fluorescent constituents from the capsule or matrix.
The present invention also provides methods for producing capsules or matrices that preferably emit two or more signals of precisely controlled intensities. This is accomplished by encapsulating soluble or insoluble fluorescent materials within a barrier material or by dispersing within a non-leakable matrix, the outer surface of which constitutes the barrier per se. Fluorescent materials may be in a number of forms, including dye absorbed in small polymeric spheres, granules, fibers, dye dissolved in a solvent, amorphous powders, or crystals, such as CdS.
It is preferable that encapsulation material chosen for application are compatible with the application; that is, if the particles are to be used in a particular solvent, the shell material must be stable in that solvent. The outer coating layer (shell) of the present invention preferably comprises between about 1-20% by weight of the interior matrix.
Examples of potentially useful and preferable shell materials are: gelatin, gum arabic, collagen, casein, polystyrene, and other art-known polymeric materials that will serve to deter migration of the fluorescent materials from the capsule. Such materials are well known in the art, including but not limited to: chitosan, polycarboxylated polymer, hydrophilic gums and hydrophilic mucilloids such as agar, alginic acid, calcium polycarbophil, cellulose, carboxymethylcellulose sodium, carrageenan, chondrus, glucomannan, polymannose acetate, guar gum, karaya gum, kelp, methylcellulose, plantago seed (psyllium), polycarbophil tragacanth, pectin, starch, tragacanth gum, xanthan gum or acidic fractions thereof, monoalkylene glycol monoester of methacrylic. acid, polyalkylene glycol monoester of methacrylic acid, monoalkylene glycol monoester of a crylic acid, polyalkylene glycol monoester, N-alkyl substituted acrylamide, N,N-dialkyl substituted acrylamide, N-alkyl substituted methacrylamide, N,N-dialkyl substituted methacrylamide, N-vinylpyrrolidone, alkyl substituted N-vinylpyrrolidone, vicinal epoxy alkyl 2-alkenoate, and combination thereof among them or with many other materials. For example, in addition to polystyrene,-polymeric materials will include but are not limited to brominated polystyrene, polyacrylic acid, polyacrylonitrile, polyamide, polyacrylamide, polyacrolein, polybutadiene, polycaprolactone, polycarbonate, polyester, polyethylene, polyethylene terephthalate, polydimethylsiloxane, polyisoprene, polyurethane, polyvinylacetate, polyvinylchloride, polyvinylpyridine, polyvinylbenzylchloride, polyvinyltoluene, polyvinylidene chloride, polydivinylbenzene, polymethylmethacrylate, polylactide, polyglycolide, poly(lactide-co-glycolide), polyanhydride, polyorthoester, polyphosphazene, polysulfone, or combinations thereof are acceptable as well. Other materials such as carbohydrate, e.g., hydroxyethyl cellulose, proteinaceous polymers, polypeptides, lipids (liposomes), metal, resin, latex, rubber, silicone, e.g., polydimethyldiphenyl siloxane, glass, ceramic and the like are equally suitable. The various encapsulation techniques using these materials are well documented in encapsulation art and are familiar to those skilled in the art.
The fluorescent emission profile can be specified by two methods, each of which accomplishes this by manipulating the amount of fluorescent material in the capsule. One technique uses capsule size to dictate the fluorescent emission. A mixture of soluble and/or insoluble fluorescent particles at specific concentrations is prepared, then agitation is applied during the encapsulation process. Thus, in a preferred particle making method, numerous sets of differently sized microcapsules containing the fluorescent substances are made by varying the agitation rate. In this manner, for a given starting concentration of fluorescent substances, the larger capsules would have more intense fluorescent emissions than smaller capsules. Another advantage is that particle size serves as an additional parameter with which various capsule populations are differentiated. The preferred size range of capsules is anywhere from about 1 nanometer (nm) to about 10 millimeters (mm). A more preferred size range is from about 1 micrometer (micron) to about millimeter (mm) or 1,000 microns.
Another preferred technique to create multiple, distinguishable populations of fluorescent particles is to simply vary the concentration of fluorescent emitters in uniformly sized capsules. This is accomplished by diluting the fluorescent phase with non-fluorescent material. By varying the degree of dilution of a given fluorescent mixture, as well as varying the concentrations of fluorescent materials relative to each other, a large population of distinguishable particles is manufactured.
A large number of materials and techniques can be used to form the microcapsules, which are familiar to those skilled in the art. A variety of microencapsulation methods and compositions are known in the art. These compositions are primarily used in pharmaceutical formulations, for example, to mask the taste of bitter drugs, formulate prolonged dosage forms, separate incompatible materials, protect chemicals from moisture or oxidation, or modify the physical characteristics of the material for ease of handling and/or processing. Typical pharmaceutical encapsulation compositions include, e.g., gelatin, polyvinyl alcohol, ethylcellulose, cellulose acetatephthalate and styrene maleic anhydride. See Remington""s Pharmaceutical Sciences, Mack Publishing Co., Easton Pa. (1990). Microencapsulation has also been applied in the treatment of diseases by transplant therapy. Exemplary methods and materials are described hereinafter.
The encapsulation materials chosen for application must be compatible with the application; that is, if the particles are to be used in a particular solvent, the shell material must be stable in that solvent. The outer coating layer (shell) of the present invention preferably comprises between about 1-20% by weight of the interior matrix.
Additives useful as filling the matrix composition of the present invention include but are not limited to: tetrakis[methylene 3,-(3xe2x80x25xe2x80x2-di-tertbutyl-4xe2x80x3-hydroxphenyl) propionate]methane, octadecyl 3-(3xe2x80x3,5xe2x80x3-di-tert-butyl-4xe2x80x3-hydroxyphenyl) propionate, distearyl-pentaerythritoldiproprionate, thiodiethylene bis-(3,5-ter-butyl-4-hydroxy) hydrocinnamate, (1,3,5-trimethyl-2,4,6-tris[3,5-di-tert-butyl-4-hydroxybeizyl]benzene), 4,4xe2x80x3-methylenebis(2,6-di-tert-butylphenol), steraric acid, oleic acid, stearamide, behenamide, oleamide, erucamide, N,Nxe2x80x3-ethylenebisstearamide, N,Nxe2x80x3-ethylenebisoleamide, sterryl erucaide, erucyl erucamide, oleyl palmitamide, stearyl stearamide, erucyl stearamide, waxes (e.g. polyethylene, polypropylene, microcrystalline, carnauba, paraffin, montan, candelila, beeswax, ozokerite, ceresine, and the like), fatty acids selected from stearic acid, lauric acid, myristic acid, palmitic acid and the like, metal stearates selected from calcium stearate, magnesium stearate, zinc stearate, aluminum stearate and the like. Minor amounts of other polymers and copolymers can be melt-blended with the styrene-ethylene-butylene-styrene block copolymers mentioned above without substantially decreasing the desired properties. Such polymers include (SBS) styrene-butadiene-styrene block copolymers, (SIS) styrene-isoprene-styrene block copolymers, (low styrene content SEBS) styrene-ethylene-butylene-styrene block copolymers, (SEP) styrene-ethylene-propylene block copolymers, (SB)n styrene-butadiene and (SEB)n, (SEBS)n, (SEP)n, (SI)n styrene-isoprene multi-arm, branched, and star shaped copolymers and the like. Still, other homopolymers can be utilized in minor amounts; these include: polystyrene, polybutylene, polyethylene, polypropylene and the like.
Examples of potentially useful and preferable shell materials are: gelatin, gum arabic, collagen, casein, polystyrene, and other art-known polymeric materials that will serve to deter migration of the fluorescent materials from the capsule. Such materials are well known in the art, including but not limited to: chitosan, polycarboxylated polymer, hydrophilic gums and hydrophilic mucilloids such as agar, alginic acid, calcium polycarbophil, carboxymethylcellulose sodium, carrageenari, chondrus, glucomannan, polymannose acetate, guar gum, karaya gum, kelp, methylcellulose, plantago seed (psyllium), polycarbophil tragacanth, pectin, tragacanth gum, xanthan gum or acidic fractions thereof, monoalkylene glycol monoester of methacrylic acid, polyalkylene glycol monoester of methacrylic acid, monoalkylene glycol monoester of crylic acid, polyalkylene glycol monoester, N-alkyl substituted acrylamide, N,N-dialkyl substituted acrylamide, N-alkyl substituted methacrylamide, N,N-dialkyl substituted methacrylamide, N-vinylpyrrolidone, alkyl substituted N-vihylpyrrolidone, vicinal epoxy alkyl 2-alkenoate, and combination thereof among them or with many other materials. For example, in addition to polystyrene, polymeric materials will include but are not limited to brominated polystyrene, polyacrylic acid, polyacrylonitrile, polyamide, polyacrylamide, polyacrolein, polybutadiene, polycaprolactone, polycarbonate, polyester, polyethylene, polyethylene terephthalate, polydimethylsiloxane, polyisoprene, polyurethane, polyvinylacetate, polyvinylchloride, polyvinylpyridine, polyvinylbenzylchloride, polyvinyltoluene, polyvinylidene chloride, polydivinylbenzene, polymethylmethacrylate, polylactide, polyglycolide, poly(lactide-co-glycolide), polyanhydride, polyorthoester, polyphosphazene, polysulfone, or combinations thereof are acceptable as well. Other materials such as carbohydrate, e.g., hydroxyethyl cellulose, proteinaceous polymers, polypeptides, lipids (liposomes), metal, resin (natural resins such as gum rosin, wood rosin, and tall oil rosin, shellac, copal, damrnmar, gilsonite and zein; semi-synthetic resins such as hardened rosin, ester gum and other rosin esters, maleic acid resin, fumaric acid resin, dimer rosin, polymer rosin, rosin-modified phenol resin, synthetic resins such as phenolic resin, xylenic resin, urea resin, melamine resin, ketone resin, coumarone-indene resin, petroleum resin, terpene resin, alkyl resin, polyarnide resin, acrylic resin, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral (butyral resin), polyvinyl pyrrolidone, chlorinated polypropylene, styrene resin, epoxy resin and polyurethane), wax (e.g. polyethylene, polypropylene, microcrystalline, carnauba, paraffin, montan, candelila, beeswax, ozokerite, ceresine), latex, rubber (cyclized rubber, rubber chloride), silicone, e.g., polydimethyldiphenyl siloxane, glass, ceramic and the like are equally suitable. The various encapsulation techniques using these materials are well documented in encapsulation art and are familiar to those skilled in the art.
The presently preferred material for forming the matrix of capsules is polysaccharide gums, either natural or synthetic, of the type which can be gelled to form a shape retaining mass by being exposed to a change in conditions such as a pH change, temperature change, or by being exposed to cations such as Ca2+ or Na+. Thereafter, core or matrix material is permanently xe2x80x9ccross-linkedxe2x80x9d or hardened by polymers containing reactive groups such as aldehyde, amine or imine groups which can react with essentially monomeric constituents. Thus, included within the term xe2x80x9cencapsulation,xe2x80x9d are compositions which are coated, insofar as the coating or shell provides a physical barrier.
xe2x80x9cCross-linkingxe2x80x9d as used herein, refers to the linking of two or more chains of polymer molecules, by the formation of a bridge between the molecules composed of either a chemical bond, an element, a group or a compound. The terms xe2x80x9cparticlexe2x80x9d, xe2x80x9cmicroparticlexe2x80x9d, xe2x80x9cbeadxe2x80x9d as used herein, refer to an encapsulated composition, so that each capsule encapsulating such particles ranges in size from about 1 nm to about 10 mm in diameter. More preferably, such capsules range from about 1 micron to about 1,000 microns in diameter.
Fluorescent dyes used in this invention are known in the art and may have emission wavelengths between 200 nm and 1,000 nm. However, any other suitable dye can be used. For example, the squaric acid based fluorescent dyes can be synthesized by methods described in the literature. See, for example, Sprenger et al., Angew. Chem., 79, 581 (1967); Angew. Chem., 80, 541 (1968); and Maaks et al., Angew Chem. Intern. Edit., 5, 888 (1966), incorporated herein by reference in their-entirety. Additionally, unsymmetrically substituted squaric acid compounds can be synthesized by methods such as those described by Law et al., J. Org. Chem. 57, 3278,(1992), incorporated herein by reference in its entirety. Specific methods of making some of such dyes are well known in the art and can be found for example in U.S. Pat. Nos. 5,795,981; 5,656,750; 5,492,795; 4,677,045; 5,237,498; and 5,354,873, incorporated herein by reference in their entirety. The practical use of above described fluorescent dyes, e.g., phthalocyanines, 2,3-naphthalocyanines, squaraines and croconic acid derivatives is disclosed in U.S. Pat. No. 5,525,516 issued to Krutak et al., incorporated herein by reference in its entirety. These dyes may contain methine groups and their number influences the spectral properties of the dye. The monomethine dyes that are pyridines and typically have blue to blue-green fluorescence emission, while quinolines have green to yellow-green fluorescence emission. The trimethine dye analogs are substantially shifted toward red wavelengths, and the pentamethine dyes are shifted even further, often exhibiting infrared fluorescence emission (see for example U.S. Pat. No. 5,760,201) incorporated herein by reference in its entirety.
Related dyes can be further selected from cyclobutenedione derivatives, substituted cephalosporin compounds, fluorinated squaraine compositions, symmetrical and unsymmetrical squaraines, alkylalkoxy squaraines, or squarylium compounds. Some of these dyes can fluoresce at near infrared as well as at infrared wavelengths that would effectively expand the range of emission spectra up to about 1,000 nm. In addition to squaraines, i.e., derived from squaric acid, hydrophobic dyes such as phthalocyanines and naphthalocyanines can be also selected as operating at longer wavelengths. Other classes of fluorochromes are equally suitable for use as dyes according to the present invention. Non-limiting examples-of some of these dyes are listed herein: 3-Hydroxypyrene 5,8,10-Tri Sulfonic acid, 5-Hydroxy Tryptamine, 5-Hydroxy Tryptamine (5-HT), Acid Fuchsin, Acridine Orange, Acridine Red, Acridine Yellow, Acriflavin, AFA (Acriflavin Feulgen SITSA), Alizarin Complexon, Alizarin Red, Allophycocyanin, ACMA, 4-dicycano -methylene-2-methyl-6-(p-dimethylaminostyryl)4H-pyran, fluorescent chelates of lanthanide ions, for example ions of Terbium, Samarium, and, Europium, Aminoactinomycin D, Aminocoumarin, Anthroyl Stearate, Aryl- or Heteroaryl-substituted Polyolefin, Astrazon Brilliant Red 4G, Astrazon Orange R, Astrazon Red 6B, Astrazon Yellow 7 GLL, Atabrine, Auramine, Aurophosphine, Aurophosphine G, BAO 9 (Bisaminophenyloxadiazole), BCECF, Berberine Sulphate, Bisbenzamide, BOBO 1, Blancophor FFG Solution, Blancophor SV, Bodipy F1, BOPRO 1, Brilliant Sulphoflavin FF, Calcien Blue, Calcium Green, Calcofluor RW Solution, Calcofluor White, Calcophor White ABT Solution, Calcophor White Standard Solution, Carbocyanine, Carbostyryl, Cascade Blue, Cascade Yellow, Cate cholamine, Chinacrine, Coriphosphine O, Coumarin, Coumarin-Phalloidin, CY3.1 8, CY5.1 8, CY7, Dans (1-Dimethyl Amino Naphaline 5 Sulphonic Acid), Dansa (Diamino Naphtyl Sulphonic Acid), Dansyl NHCH3, DAPI, Diamino Phenyl Oxydiazole (DAO), Dimethylamino-5-Sulphonic acid, Dipyrrometheneboron Difluoride, Diphenyl Brilliant Flavine 7GFF, Dopamine, Eosin, Erythrosin ITC, Ethidium Bromide, Euchrysin, FIF (Formaldehyde Induced Fluorescence), Flazo Orange, Fluo 3, Fluorescamine, Fura-2, Genacryl Brilliant Red B, Genacryl Brilliant Yellow 10GF, Genacryl Pink 3G, Genacryl Yellow 5GF, Gloxalic Acid, Granular Blue, Haematoporphyrin, Hoechst 33258, Indo-1, Intrawhite Cf Liquid, Leucophor PAF, Leucophor SF, Leucophor WS, Lissamine Rhodamine B200 (RD200), Lucifer Yellow CH, Lucifer Yellow VS, Magdala Red, Marina Blue, Maxilon Brilliant Flavin 10 GFF, Maxilon Brilliant Flavin 8 GFF, MPS (Methyl Green-Pyronine Stilbene), Mithramycin, NBD Amine, Nile Red, Nitrobeinzoxadidole, Noradrenaline, Nuclear Fast Red, Nuclear Yellow, Nylosan Brilliant Flavin E8G, Oregon Green, Oxazine, Oxazole, Oxadiazole, Pacific Blue, Pararosaniline (Feulgen), Phorwite AR Solution, Phorwite BKL, Phorwite Rev, Phorwite RPA, Phosphine 3R, Phthalocyanine, Phycoerythrin R, Polyazaindacene Pontochrome Blue Black, Porphyrin, Primuline, Procion Yellow, Propidium Iodide, Pyronine, Pyronine B, Pyrozal Brilliant Flavin 7GF, Quinacrine Mustard, Rhodamine 123, Rhodamine 5 GLD, Rhodamine 6G, Rhodamine B, Rhodamine B 200, Rhodamine B Extra, Rhodamine BB, Rhodamine BG, Rhodamine WT, Rose Bengal, Serotonin, Sevron Brilliant Red 2B, Sevron Brilliant Red 4G, Sevron Brilliant Red B, Sevron Orange, Sevron Yellow L, SITS (Primuline), SITS (Stilbene Isothiosulphonic acid), Stilbene, Snarf 1, sulpho Rhodamine B Can C, Sulpho Rhodamine G Extra, Tetracycline, Texas Red, Thiazine Red R, Thioflavin S, Thioflavin TCN, Thioflavin 5, Thiolyte, Thiozol Orange, Tinopol CBS, TOTO 1, TOTO 3, True Blue, Ultralite, Uranine B, Uvitex SFC, Xylene Orange, XRITC, YO PRO 1, or combinations thereof.
One skilled in the art would certainly know which one to select among such dyes as long as desired emission and absorption properties as well as their hydrophobic or hydrophilic properties are appropriate.
One skilled in the art would certainly know to select instead of above listed dyes so-called man-made xe2x80x9cquantum dotsxe2x80x9d or xe2x80x9csemiconductor nanocrystalsxe2x80x9d, which usually consist of sulfide (S) or selenium (Se) of various metals such as Zn, Cd, Pb, Sn, Hg, Al, Ga, In, Ti, Si, Ag, Fe, Ni or Ca. The means of making quantum dots are well known in the art as disclosed, for example, in U.S. Pat. Nos. 5,906,670; 5,888,885; 5,229,320; and 5,482,890, which are incorporated herein by way of reference. Other metals are known which can fluoresce when in a chelated form (e.g., EDTA) and may include but are not limited to metals such as Tc, In, Ga, Sc, Fe, Co, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb (e.g., U. S. Pat. Nos. 4,454,106 and 4,374,120) incorporated herein by reference in their entirety.
Furthermore, naturally occurring minerals and crystals such as Clinohedrite, Hardystonite, Willemite, Witherite, Yellow Calcite, Tan Calcite, Terlingua Calcite, Amber, Scapolite, and Eucryptite among others, are also known to fluoresce when exposed to a short-wave high-energy excitation light (detailed list of some of such minerals can be found in U.S. Pat. Nos. 4,365,153; 4,336,459; and 4,236,071, which references are incorporated herein by way of reference). Specifically, minerals that are known to fluoresce in a blue spectrum include but are not limited to Betiitoite, Hydrozincite, and Scheelite; those that emit green fluorescence include Chalcedony Rose, Hyalite Opal, Youngite, those that emit red fluorescence include Eucryptite, those that emit orange fluorescence include Halite, Svabite-Tilisite. There are also some minerals, which may, for example, emit fluorescent light in two separate light spectra such as Phlogopite/Diopside (yellow/blue colors respectively). Such minerals are used as such in crystalline form or can be ground into fine powders.
Preferably, fluorescent materials of the invention are present in the form of spherical microparticles or crystals or nanocrystals such as quantum dots. Physical shapes other than spherical particles, crystals, and powders can be incorporated within a shell barrier. One skilled in the art may utilize fluorescent fibers such as disclosed, for example, in U.S. Pat. No. 4,921,280, as incorporated herein by way of reference. Encapsulated fluorescent materials of the invention may also include light-excitable materials such as used in liquid crystal display (LCD) devices, which are disclosed in U.S. Pat. Nos. 3,998,526; 4,337,999; 4,425,029; 4,668,049; 5,039,206; and 5,052,784, as incorporated herein by way of reference.
The spectral propertiesof the fluorescent materials should be sufficientlyimilar in excitation wavelengths and intensity to fluorescein or rhodamine derivatives as to permit the use of the same flow cytometry equipment. More preferably, the dyes have the same or overlapping excitation spectra, but possess distinguishable emission spectra. Any detection system can be used to detect the difference in spectral characteristics between the two dyes, including a solid state detector, photomultiplier tube, photographic film, or eye, any of which may be used in conjunction with additional instrumentation such as a spectrometer, luminometer microscope, plate reader, fluorescent scanner, flow cytometer, or any combination thereof, to complete the detection system. Preferably, dyes are chosen such that they possess substantially different emission spectra, preferably having emission maxima separated by greater than 10 nm, more preferably having emission maxima separated by greater than 25 nm, even more preferably separated by greater than 50 nm. When differentiation between the two dyes is accomplished by visual inspection, the two dyes preferably have emission wavelengths of perceptibly different colors to enhance visual discrimination. When it is desirable to differentiate between the two dyes using instrumental methods, a variety of filters and diffraction gratings allow the respective emission maxima to be independently detected. When two dyes are selected that possess similar emission maxima, instrumental discrimination can be enhanced by insuring that both dyes"" emission spectra have similar integrated amplitudes, similar bandwidths, and the instrumental system""s optical throughput be equivalent across the emission range of the two dyes. Instrumental discrimination can also be enhanced by selecting dyes with narrow bandwidths rather than broad bandwidths, however such dyes must necessarily possess a high amplitude emission or be present in sufficient concentration that the loss of integrated signal strength is not detrimental to signal detection.